A mixture of blue and green light of respective wavelengths $4000 \AA$ and $5400 \AA$ falls normally

Question

A mixture of blue and green light of respective wavelengths $4000 \AA$ and $5400 \AA$ falls normally on an air film of $0.3 \mu \mathrm{~m}$ thickness. The film looks\

Professor PC Thomas Classes · Answer

D)When one treats thin films, say of water of oil or glass it has air above conditions are different for interference in transmission and in reflection. In reflection, as there is a further phase difference of $\pi / 2$, when reflection takes place from air film interface.\ $2 \mu \operatorname{tcos} \mathrm{r}=\mathrm{n} \lambda$ will eliminate $\lambda$ for that n .\ If it is normal incidence for reflection, $2 \mu \mathrm{t}=\lambda$ will eliminate reflection of $\lambda$. If $\mu=1, \lambda=6000 \mathrm{~A}^{\circ}$, therefore green is eliminated as per answer given assuming the question is for reflection. But the air film could have been changed and the question more\ specific as observations are in air and the film is different. Otherwise the formula used will not be correct.\